1. Field of the Invention
The present invention relates to a magnetic detecting element comprising pinned magnetic layers adjacent to both end surfaces of a free magnetic layer through nonmagnetic material layers so that a sense current flows in a direction crossing the interfaces between the free magnetic layer and the nonmagnetic material layers and the interfaces between the pinned magnetic layers and the nonmagnetic material layers. Particularly, the present invention relates to a magnetic detecting element capable of effectively improving a rate ΔR/R of change in resistance.
2. Description of the Related Art
With improvements in the linear recording density of a recording medium there have recently been demands for a shorter gap length. The gap length is defined by a distance between upper and lower shields. The upper and lower shields comprise a magnetic material and are respectively formed at the top and bottom of a reproducing magnetic detecting element.
The mainstream of conventional reproducing magnetic heads for reading a signal magnetic field from a magnetic recording medium is a spin-valve GMR magnetic detecting element comprising a free magnetic layer comprising a thin film comprising a ferromagnetic material, and a pinned magnetic layer laminated thereon through a nonmagnetic material layer in a direction perpendicular to the film plane. However, in the system in which the free magnetic layer, the nonmagnetic material layer and the pinned magnetic layer are laminated in the direction perpendicular to the film plane, it is difficult to further shorten the gap length.
Therefore, there has been proposed a magnetic detecting element in which pinned magnetic layers face both end surfaces of a free magnetic layer through nonmagnetic material layers so that a sense current flows in a direction crossing the interfaces between the free magnetic layer and the nonmagnetic material layers and the interfaces between the pinned magnetic layers and the nonmagnetic material layers, as shown in FIG. 13.
FIG. 13 is a partial sectional view showing a magnetic detecting element, as viewed from a surface facing a recording medium. In the magnetic detecting element shown in FIG. 13, a free magnetic layer 4 comprising a soft magnetic material such as NiFe or the like is formed in a substantially trapezoidal shape on a lower shield layer 1 comprising a magnetic material through a gap layer 2 comprising an insulating material and an underlying layer 3 comprising Cr or Ta. A nonmagnetic material layer 5 is formed to extend from each end surface 4a of the free magnetic layer 4 to each of both side portions of the lower gap layer 2 on both sides of the free magnetic layer 4. Furthermore, pinned magnetic layers 6 each comprising a soft magnetic material such as NiFe or the like are formed in contact with the respective nonmagnetic material layers 5. Also, antiferromagnetic layers 7 are laminated on the respective pinned magnetic layers 6 so that an exchange coupling magnetic field is produced at each of the interfaces between the pinned magnetic layers 6 and the nonmagnetic antiferromagnetic layers 7 to pin the magnetization direction of each pinned magnetic layer 6 in the direction antiparallel to the Y direction shown in the drawing. Furthermore, an upper gap layer 8 comprising an insulating material, and an upper shield layer 9 comprising a magnetic material are formed on the free magnetic layer 4 and the antiferromagnetic layers 7.
A sense current flows through the pinned magnetic layers 6, the nonmagnetic material layers 5 and the free magnetic layer 4 in the X direction shown in the drawing. Namely, the sense current flows in a direction crossing the interfaces between the free magnetic layer 4 and the nonmagnetic material layers 5 and the interfaces between the pinned magnetic layers 6 and the nonmagnetic material layers 5. The free magnetic layer 4 is put into a single magnetic domain state in the X direction. When an external magnetic field is applied in the Y direction, the magnetization direction of the free magnetic layer 4 rotates to the Y direction. When the magnetization direction of the free magnetic layer 4 rotates in a state wherein the magnetization direction of each pinned magnetic layer 6 is pinned in the direction antiparallel to the Y direction, the resistance of the magnetic detecting element changes. The change in the resistance of the magnetic detecting element is taken out as a current change or voltage change to detect the external magnetic field. A magnetic detecting element having the above-described structure is disclosed in U.S. Pat. Nos. 6,396,668B1 and 6,411,478B1 and Japanese Unexamined Patent Application Publication No. 2001-319313. U.S. Pat. No. 6,396,668B1 discloses a spin-vale GMR magnetoresistive element, and U.S. Pat. No. 6,411,478B1 and Japanese Unexamined Patent Application Publication No. 2001-319313 disclose a spin-valve tunneling magnetoresistive element (TMR).
In the magnetic detecting element having the structure shown in FIG. 13, the sense current flows in the direction crossing the interfaces between the free magnetic layer 4 and the nonmagnetic material layers 5 and the interfaces between the pinned magnetic layers 6 and the nonmagnetic material layers 5. Therefore, in the magnetic detecting element shown in FIG. 13, a change in resistance due to an external magnetic field is thought to be mainly derived from bulk scattering of conduction electrons in the free magnetic layer 4 and the pinned magnetic layers 6. Therefore, a greater change ΔR in resistance than a magnetoresistive effect derived from scattering of the sense current at the interfaces between the free magnetic layer and the nonmagnetic material layers or the interfaces between the pinned magnetic layers and the nonmagnetic material layers can be obtained.
Also, in a magnetic detecting element utilizing spin-dependent bulk scattering of conduction electrons, the resistance R of the element itself must be increased to some extent for detecting a magnetic field. In the magnetic detecting element having the shape shown in FIG. 13, the sense current flows in the direction crossing the interfaces between the end surfaces 4a of the free magnetic layer 4 and the nonmagnetic material layers 5 and the interfaces between the inner end surfaces 6a of the pinned magnetic layers 6 and the nonmagnetic material layers 5, and thus the sectional area of the sense current path can be decreased. Therefore, the resistance R of the magnetic detecting element can be increased, as compared with the magnetic detecting element in which the sense current flows in the direction perpendicular to the film plane of each of the free magnetic layer 4, the nonmagnetic material layers 5 and the pinned magnetic layers 6.
In the magnetic detecting element in which the sense current flows in the direction perpendicular to the film plane of each of the free magnetic layer 4, the nonmagnetic material layers 5 and the pinned magnetic layers 6, the thickness of each magnetic layer must be increased for attaining a sufficient change in magnetoresistance. However, in the magnetic detecting element having the shape shown in FIG. 13, the current flows in parallel with the film plane, and thus a change in magnetoresistance can easily be increased because the dimension of the magnetic detecting element in a direction parallel to the film plane is larger than the thickness dimension.
Furthermore, the pinned magnetic layers 6 are not laminated above or below the free magnetic layer 4 functioning as a portion for detecting a magnetic field, and thus the distance between upper and lower shields provided above and below the free magnetic layer 4 can be decreased to facilitate narrowing of the gap.
As shown in FIG. 14, when a free magnetic layer 14 has a synthetic ferrimagnetic structure in which magnetic layers 11 and 13 comprising a soft magnetic material are laminated with a nonmagnetic intermediate sub-layer 12 provided therebetween, the obtained effect is the same as that obtained by decreasing the thickness of the free magnetic layer, and the effective magnetic moment per unit area is decreased to facilitate a change in magnetization of the free magnetic layer. A conventional magnetic detecting element comprises the free magnetic layer 14 including the magnetic layers 11 and 13 both of which comprise NiFe or CoFe. The nonmagnetic intermediate sub-layer 12 comprises Ru.
However, the magnetic detecting element shown in FIG. 14 causes the following problem.
In the magnetic detecting element shown in FIG. 14, magnetization of each pinned magnetic layer 16 is pinned in the direction antiparallel to the Y direction shown in the drawing.
The magnetic layer 11 of the free magnetic layer 14 is put into a single magnetic domain state in the X direction shown in the drawing, and magnetization of the magnetic layer 13 is oriented in the direction antiparallel to the X direction due to a RKKY interaction through the nonmagnetic intermediate sub-layer 12. Of the magnetic layers 11 and 13 of the free magnetic layer 14, the effective magnetic moment (the product of saturation magnetization Ms and thickness t) per unit area of the magnetic layer 11 is larger than that of the magnetic layer 13.
For example, when an external signal magnetic field is applied to the magnetic detecting element shown in FIG. 14 in the Y direction, magnetization of the magnetic layer 11 having the larger effective magnetic moment per unit area rotates to the Y direction. At the same time, the magnetization direction of each pinned magnetic layer 6 approaches the direction antiparallel to the magnetization direction of the magnetic layer 11, and thus the electric resistance for the current flowing from the pinned magnetic layers 6 to the magnetic layer 11 through the nonmagnetic material layers 5 is increased.
However, when the magnetization of the magnetic layer 11 rotates to the Y direction, magnetization of the magnetic layer 13 rotates to the direction antiparallel to the Y direction, and thus the magnetization direction of each pinned magnetic layer 6 approaches a direction parallel to the magnetization direction of the magnetic layer 13. Therefore, the electric resistance for the current flowing from the pinned magnetic layers to the magnetic layer 13 through the nonmagnetic material layers 5 is decreased.
Namely, in the magnetic detecting element shown in FIG. 14, an increase in the electric resistance for the current flowing from the pinned magnetic layers 6 to the magnetic layer 11 through the nonmagnetic material layers 5 is canceled by a decrease in the electric resistance for the current flowing from the pinned magnetic layers 6 to the magnetic layer 13 through the nonmagnetic material layers 5, thereby decreasing a change ΔR in resistance of the magnetic detecting element.
As shown in FIG. 26, when each of pinned magnetic layers 14 has a synthetic ferrimagnetic structure in which magnetic layers 11 and 13 each comprising a soft magnetic material are laminated with a nonmagnetic intermediate sub-layer 12 provided therebetween, magnetization of each pinned magnetic layer 14 can be strongly pinned. Therefore, magnetic detection output can be increased, and output symmetry can be improved. A conventional magnetic detecting element comprises the pinned magnetic layers 14 each including the magnetic layers 11 and 13 both of which comprise NiFe or CoFe. The nonmagnetic intermediate sub-layers 12 comprise Ru.
However, the magnetic detecting element shown in FIG. 26 causes the following problem.
In the magnetic detecting element shown in FIG. 26, magnetization of the free magnetic layer 4 is put into a single-magnetic-domain state in the X direction shown in the drawing.
Magnetization of the magnetic layer 11 of each pinned magnetic layer 14 is pinned in the direction antiparallel to the Y direction shown in the drawing due to an exchange coupling magnetic field with the antiferromagnetic layer 7, and magnetization of the magnetic layer 13 is oriented in the Y direction due to a RKKY interaction through the nonmagnetic intermediate sub-layer 12. Of the magnetic layers 11 and 13 of each pinned magnetic layer 14, the effective magnetic moment (the product of saturation magnetization Ms and thickness t) per unit area of the magnetic layer 13 is larger than that of the magnetic layer 11.
For example, when an external signal magnetic field is applied to the magnetic detecting element shown in FIG. 26 in the Y direction, magnetization of the free magnetic layer 4 rotates to the Y direction. At the same time, the magnetization direction of the free magnetic layer 4 approaches the direction antiparallel to the magnetization direction of the magnetic layers 11, and thus the electric resistance for the current flowing from the magnetic layers 11 to the free magnetic layer 4 through the nonmagnetic material layers 5 is increased.
However, when the magnetization of the free magnetic layer 4 is rotated to the Y direction, the magnetization direction of the free magnetic layer 4 comes close to a direction parallel to the magnetization direction of the magnetic layers 13. Therefore, the electric resistance for the current flowing from the magnetic layers 13 to the free magnetic layer 4 through the nonmagnetic material layers 5 is decreased.
Namely, in the magnetic detecting element shown in FIG. 26, an increase in the electric resistance for the current flowing from the magnetic layers 11 to the free magnetic layer 4 through the nonmagnetic material layers 5 is canceled by a decrease in the electric resistance for the current flowing from the magnetic layers 13 to the free magnetic layer 4 through the nonmagnetic material layers 5, thereby decreasing a change ΔR in resistance of the magnetic detecting element.